Data on read-only storage media may not be modified. One example of such read-only media are prerecorded discs, e.g. Blu-ray discs (BDP).
Storage media, particularly optical discs, have usually unique identification labels. It is common that disc players may have integrated harddisk drives (HDD). Within an optical disc player, a Playback Control Engine (PCE) processes the data read from the disc. The data scope of a PCE is the disc. The playback process is controlled by a so-called Movie Module, which via an application interface (API) is connected to the PCE.
The data on the disc usually structured in a directory tree that is often standardized. E.g. for BDP the directory tree of a particular movie contains one folder for the playlist, one folder with streaming data and one folder for the clipinfo, describing the stream data structure. AV data on a BDP disc are contained in streams, which are multiplexed into a so-called main multiplex.
In this application, the term “directory tree” is used for a complete directory structure as well as for a particular branch of a directory structure, even hierarchical branches, when referring to rewritable media.